In general, it is general to deposit N-base coated hard alloys, such as TiN, TiCN, and TiAlN, using an arc process or sputtering, which are physical vapor deposition, in order to improve abrasion resistance of indexable inserts/abrasion resistant tools. The TiAlN coated hard alloy is recently the most interested film in the metal cutting field because the abrasion resistance the highest under high temperature in the films.
However, although the TiAlN has high abrasion resistance due to high hardness, the shock resistance is lower than the TiN and TiCN films, such that it is generally not suitable to works with shock or middle/low speed works, while the TiN and TiCN may show the same behaviors, depending on work conditions.
Although it is possible to improve the abrasion resistance or the shock resistance by changing the type of deposition and the deposition factors, it is substantially difficult to improve both of the properties. In general, the abrasion resistance and the shock resistance are opposite properties and difficult to be simultaneously improved, such that the properties depend on the regions and the uses of the films; however, in general, both of the abrasion resistance and the shock resistance are required, such that it is substantially impossible to deposit a film having properties suitable for various workpieces under various machining conditions.
For this reason, the applicant(s) has recently proposed a secondary method for reducing the ratio of breakage due to mechanical shock by combining a TiN film or other films having good lubricity with a TiAlN film having good abrasion resistance, rather than improving the properties of the film itself, in Korean Patent Application No. 200343513, filed on 30 Jun., 2003.
However, the deposition time increases due to reduction of the evaporation source because an evaporation source for depositing the lubricant film is required, other than the evaporation source for depositing the main film.
Further, the tools are broken in continual cutting, because the basic properties of the film itself are not improved.
The applicant(s) has proposed “A TiAlN-based multi-layer with antiwear and antishockcoated to cutting tool” in Korean Patent Registration No. 100622912, in order to solve the problems, but it has a limit in increasing abrasion resistance and oxidation resistance.
On the other hand, high-speed machining is required to improve productivity, according to current industrial and technical trends, such that indexable inserts having a TiAlN film having more improved oxidation resistance, instead of TiN and TiCN, are commonly used.
Further, films have been continuously developed with the increase of cutting speed, and for example, a single film added with Si in an AlTiN film structure to improve oxidation resistance has been proposed in U.S. Pat. No. 5,580,653, while a multi-layer structure having one cycle of two films, depending on the contents of Si, in the second film structure has been proposed in U.S. Pat. No. 6,586,122.
However, in those patents, since the film containing Si has considerably high compressive stress as compared with the film without Si, it has large brittleness. Further, the film containing Si is easily separated when being directly deposited on an indexable insert, because of the high compressive stress.
There has been proposed a technology implementing a multi-layer film by depositing a film without Si on an indexable insert and applying different Si proportion to improve only the abrasion resistance and oxidation resistance, in order to solve the problems.
The technology, however, also has a problem in that two or more target sources with different Si content should be provided in a PVD coating apparatus and the targets with Si are expensive, such that it is economically disadvantageous.
Therefore, it is the most important to implement a multi-layer film structure that is economically advantageous by providing only one target with Si or Cr and has chipping resistance required by the patents described above or more improved chipping resistance, and a multi-layer film of which both of abrasion resistance and oxidation resistance are improved, in addition to the properties of the above multi-layer film structure.